Re: [PATCH 7/9] ptrace: Simplify the wait_task_inactive call in ptrace_check_attach

[Peter Zijlstra]

On Thu, Apr 28, 2022 at 04:57:50PM +0200, Oleg Nesterov wrote:

> > Shouldn't we then switch wait_task_inactive() so have & matching instead
> > of the current ==.
> 
> Sorry, I don't understand the context...

This.. I've always found it strange to have wti use a different matching
scheme from ttwu.

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f259621f4c93..c039aef4c8fe 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3304,7 +3304,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
 		 * is actually now running somewhere else!
 		 */
 		while (task_running(rq, p)) {
-			if (match_state && unlikely(READ_ONCE(p->__state) != match_state))
+			if (match_state && unlikely(!(READ_ONCE(p->__state) & match_state)))
 				return 0;
 			cpu_relax();
 		}
@@ -3319,7 +3319,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
 		running = task_running(rq, p);
 		queued = task_on_rq_queued(p);
 		ncsw = 0;
-		if (!match_state || READ_ONCE(p->__state) == match_state)
+		if (!match_state || (READ_ONCE(p->__state) & match_state))
 			ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
 		task_rq_unlock(rq, p, &rf);